It became apparent during the development of the HST archive at the CADC and ECF, that the usefulness and efficency of the archive would be increased if archive users had the ability to preview the image and spectral data stored in the archive. The CADC and ECF have designed a system which generates compressed data for selected "scientifically useful" datasets and stores the compressed "preview" data in a relational database system. We also have extended the STARCAT archive interface to allow users to retrieve and view any dataset in the preview database. Since the successful creation of the HST preview database, the CADC has generated preview data for various other archives. This paper describes the preview data format, the processing procedures developed to generate and store the preview data, and the software developed to display the preview data on an X display. The paper will also describe the archives for which we have generated preview data, and the archives for which we hope to generate preview data in the future.